Bond strength of near-surface mounted FRP strip-to-concrete joints

The retrofitting technique of near-surface mounting (NSM) fiber-reinforced polymer (FRP) bars/strips is receiving more attention recently due to a number of advantages over the externally bonded technique. However, there is insufficient data available in the existing literature to quantify the intermediate crack (IC) debonding mechanism of reinforced concrete members retrofitted with longitudinal NSM strips. As it is recognized that simple push-pull specimens simulate the IC debonding mechanism observed in retrofitted flexural members, this paper presents the results of a series of 36 push-pull tests using NSM strips to quantify the bond strength of such FRP-to-concrete joints. It is proposed that the confinement effect of the concrete surrounding the interface debonding crack improves the shear stress transfer mechanism resulting in higher debonding plate strains compared with externally bonded plates. A nonlinear statistical analysis of the experimental data was undertaken to develop a model to predict the maximum axial plate force for IC debonding, taken at a critical bonded length of 200 mm.